1. Field of the Invention
The present invention relates to a boat having a steering system and, more particularly relates to a steering system having an electric actuator.
2. Description of the Related Art
In conventional boat, the boat is steered in response to operation of the steering wheel. Japanese Patent Document No. JP-A-2005-254848 discloses an electric actuator that is actuated as an operator operates the steering wheel. An external force to the boat is detected during such steering, and a reaction torque is applied to the steering wheel based on the detected external force. Accordingly, the operator can feel the external force to the boat due to, for example, a water current, directly through the steering wheel, and thus can recognize the movement of the boat corresponding to such external force so as to react quickly.
When such a boat is under no external force, an operation feel of the steering wheel can be lighter. Unfortunately, when larger output is required for direction guide member deflection (high direction guide member deflection torque), and when the steering wheel is operated faster, output from the steering motor (electric actuator) becomes less responsive, resulting in a poor operation feel.
It should be noted that direction guide member deflection torque characteristics sufficient to cause direction guide member deflection may change depending on a number of conditions. For example, FIG. 7 shows a change from direction guide member deflection force characteristic line A1 to direction guide member deflection force characteristic line A2, depending on conditions such as the characteristics of the boat, a direction guide member angle, an operation speed, or the like. In such case, if a limit to the direction guide member deflection angle never changes, a direction guide member deflection force required when the direction guide member is returned after being deflected to a maximum position may exceed the motor's ability, resulting in impaired responsiveness and a poorer operation feel.
Further, as shown in FIG. 8, some motor characteristics depend on the surroundings such as temperature. For example, when the temperature becomes high the motor characteristics may change from the state shown by motor characteristic line B1 (solid line in the figure) to the state shown by motor characteristic line B2 (broken line in the figure). Since the motor characteristics at high temperatures provide lower torque, a direction guide member deflection force required may not be obtained during light temperature conditions, resulting in impaired responsiveness and a poorer operation feel.